Conventional internal combustion engines operate according to thermodynamic principles following either a two-stroke cycle or a four-stroke cycle. Both types of engines can operate using a range of fuels including gasoline, diesel, alcohol and gaseous fuels. The fuel is typically introduced into the engine using devices including carburetors and fuel injectors, for example. The fuel-air mixture can be ignited by different methods including spark ignition and compression ignition. Each engine cycle type has different merits and shortcomings with varying power density, fuel consumption, exhaust emissions, noise, vibration, engine size, weight, cost, etc.
For ordinary driving conditions, a typical vehicle is powered by an engine that is sized for the maximum performance requirement of the vehicle. For example, a passenger vehicle passing another vehicle on a hill may for a brief period utilize the maximum power of the engine. At virtually all other times, from low speed city driving to highway cruising, the power demand is a fraction of the available power. Over-sized engines with large displacements are therefore installed to meet only occasional high power demands.
The situation for large displacement working vehicles is even more dramatic. Freight hauling tractor-trailers, delivery trucks, and other vehicles are designed with engines to accommodate full loads. When traveling empty, the power requirement is substantially diminished. Similarly, marine engines often must shift from high speed or high power operation to low speed where the engine operates in idle for long periods of time. Unused displacement or over displacement results in over-sized, large engines with a multiplicity of cylinders, having a weight and complexity resulting in an unnecessary consumption of fuel and excess pollution during much of the operating time.
Existing internal combustion engines are usually limited in their operation to two-stroke or four-stroke operation. The engines have a fixed fuel distribution system, optimized for a limited range of operation. With fixed compression ratios and limited means of optimizing performance for all ranges of power, torque, and engine speed, fuel consumption is typically characterized by a specific fuel consumption curve with one point of minimum fuel consumption.
Although certain improvements to engine design have addressed these problems, for example, the use of a turbocharger for high performance operation, satisfaction of maximum power demand is at the expense of optimized fuel consumption.
Existing internal combustion engines have used switchable cam followers to actuate valves from multiple cam profiles to provide for variations in valve lash between one cam profile to the next. In a conventional system where a rocker arm or a cam follower operates with only a single cam profile, common practice is the use of a hydraulic valve adjuster that is pressurized by lubrication oil and held in a filled position using an internal check valve. These hydraulic valve adjusters have been placed in the block, in the head or in the rocker arm or cam follower itself and are very universal in their application. It is, however, inadequate in valve trains where multiple cam profiles actuate the valves through the use of rocker arms or cam followers that by some means switch from one profile to another.
In one two-stroke/four-stroke switching valvetrain (shown in U.S. Patent Application Publication 2005/0205019), the valve rocker shaft is provided with two lengthwise drillings, one to provide lubrication to all the rockers running on the shaft, and a second separate passage connecting to the rocker switching mechanism to provide control pressure to the hydraulic piston which locks and unlocks the rocker pairs. While this configuration functions well (with lubrication and control functions separate) the shaft with two small drillings is expensive and difficult to manufacture.
In addition, the response of the locking mechanism is slowed by the requirement to raise the pressure from some low level up to the spring preload threshold where the piston and locking pin may begin to move. While other switching valvetrains have overcome this difficulty by raising the lower pressure to just under the spring threshold (see U.S. Pat. No. 4,917,057) this passive arrangement has unsymmetrical response since the raising of the pressure over the threshold is rapid, but the lowering (with the higher back pressure) is slowed. In addition, the passive system cannot be controlled to vary lubrication or control pressure to suit the operating condition.
It would be desirable produce a switching mechanism for switching an engine from two-stroke to four-stroke operation wherein fuel efficiency, emissions efficiency, and power are maximized.